Carbohydrates in our diets affect the body's levels of blood glucose (blood sugar) and the hormone insulin, and insulin levels may directly or indirectly affect breast cancer risk. Aspects of carbohydrate metabolism that have been examined for a relationship to breast cancer risk can be divided into three categories: studies of the direct effect of dietary carbohydrates themselves, studies of the effect of carbohydrates that can potentially lead to large changes in blood glucose levels, and studies of the effect of insulin levels. All of these aspects of carbohydrate metabolism have an uncertain relationship to breast cancer risk. There is evidence of a weak association between type II diabetes and breast cancer risk, but this association needs to be confirmed in further research This potential association may be due to the diabetes or from diabetes-related conditions such as obesity. A moderate increase in breast cancer risk is associated with obesity in postmenopausal women. Carbohydrates from whole grains, fruits, vegetables and other high fiber foods make up the major source of calories in a healthful diet.